170 research outputs found
Quantum key distribution based on private states: unconditional security over untrusted channels with zero quantum capacity
We prove unconditional security for a quantum key distribution (QKD) protocol
based on distilling pbits (twisted ebits) [quant-ph/0309110] from an arbitrary
untrusted state that is claimed to contain distillable key. Our main result is
that we can verify security using only public communication -- via parameter
estimation of the given untrusted state. The technique applies even to bound
entangled states, thus extending QKD to the regime where the available quantum
channel has zero quantum capacity. We also show how to convert our
purification-based QKD schemes to prepare-measure schemes.Comment: Final version for IEEE TI
Entanglement fluctuation theorems
Pure state entanglement transformations have been thought of as irreversible,
with reversible transformations generally only possible in the limit of many
copies. Here, we show that reversible entanglement transformations do not
require processing on the many copy level, but can instead be undertaken on
individual systems, provided the amount of entanglement which is produced or
consumed is allowed to fluctuate. We derive necessary and sufficient conditions
for entanglement manipulations in this case. As a corollary, we derive an
equation which quantifies the fluctuations of entanglement, which is formally
identical to the Jarzynski fluctuation equality found in thermodynamics. One
can also relate a forward entanglement transformation to its reverse process in
terms of the entanglement cost of such a transformation, in a manner equivalent
to the Crooks relation. We show that a strong converse theorem for entanglement
transformations is formally related to the second law of thermodynamics, while
the fact that the Schmidt rank of an entangled state cannot increase is related
to the third law of thermodynamics. Achievability of the protocols is done by
introducing an entanglement battery, a device which stores entanglement and
uses an amount of entanglement that is allowed to fluctuate but with an average
cost which is still optimal. This allows us to also solve the problem of
partial entanglement recovery, and in fact, we show that entanglement is fully
recovered. Allowing the amount of consumed entanglement to fluctuate also leads
to improved and optimal entanglement dilution protocols.Comment: comments welcome, v2 published versio
The role of quantum information in thermodynamics --- a topical review
This topical review article gives an overview of the interplay between
quantum information theory and thermodynamics of quantum systems. We focus on
several trending topics including the foundations of statistical mechanics,
resource theories, entanglement in thermodynamic settings, fluctuation theorems
and thermal machines. This is not a comprehensive review of the diverse field
of quantum thermodynamics; rather, it is a convenient entry point for the
thermo-curious information theorist. Furthermore this review should facilitate
the unification and understanding of different interdisciplinary approaches
emerging in research groups around the world.Comment: published version. 34 pages, 6 figure
Toward physical realizations of thermodynamic resource theories
Conventional statistical mechanics describes large systems and averages over
many particles or over many trials. But work, heat, and entropy impact the
small scales that experimentalists can increasingly control, e.g., in
single-molecule experiments. The statistical mechanics of small scales has been
quantified with two toolkits developed in quantum information theory: resource
theories and one-shot information theory. The field has boomed recently, but
the theorems amassed have hardly impacted experiments. Can thermodynamic
resource theories be realized experimentally? Via what steps can we shift the
theory toward physical realizations? Should we care? I present eleven
opportunities in physically realizing thermodynamic resource theories.Comment: Publication information added. Cosmetic change
Finite-Block-Length Analysis in Classical and Quantum Information Theory
Coding technology is used in several information processing tasks. In
particular, when noise during transmission disturbs communications, coding
technology is employed to protect the information. However, there are two types
of coding technology: coding in classical information theory and coding in
quantum information theory. Although the physical media used to transmit
information ultimately obey quantum mechanics, we need to choose the type of
coding depending on the kind of information device, classical or quantum, that
is being used. In both branches of information theory, there are many elegant
theoretical results under the ideal assumption that an infinitely large system
is available. In a realistic situation, we need to account for finite size
effects. The present paper reviews finite size effects in classical and quantum
information theory with respect to various topics, including applied aspects
The Physics of Maxwell's demon and information
Maxwell's demon was born in 1867 and still thrives in modern physics. He
plays important roles in clarifying the connections between two theories:
thermodynamics and information. Here, we present the history of the demon and a
variety of interesting consequences of the second law of thermodynamics, mainly
in quantum mechanics, but also in the theory of gravity. We also highlight some
of the recent work that explores the role of information, illuminated by
Maxwell's demon, in the arena of quantum information theory.Comment: 24 pages, 13 figures. v2: some refs added, figs improve
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